1. Field of the Invention
The present invention relates generally to a method of fabricating a ceramic laminated electronic component such as a multilayer capacitor, and more particularly, to a method of fabricating a ceramic laminated electronic component having an improved step of laminating a plurality of ceramic green sheets each having electrode pastes printed thereon.
2. Description of the Prior Art
In fabricating a multilayer capacitor, a mother ceramic green sheet having electrode pastes printed in a plurality of regions is always used so as to increase productivity. More specifically, a plurality of mother ceramic green sheets are then laminated and are pressed in the direction of their thickness to obtain a mother laminated body. This mother laminated body is then cut in the direction of the thickness, to obtain a number of laminated bodies. In addition, the laminated bodies obtained are fired and provided with outer electrodes to obtain a number of multilayer capacitors.
However, in the above described mother laminated body, the upper and lower electrode pastes must be accurately overlapped with each other in the direction of the thickness; otherwise when the mother laminated body is cut in the direction of the thickness to obtain the respective laminated bodies for multilayer capacitors it is possible that the capacitance desired may not be obtained, or that the electrodes may be exposed at end surfaces of the laminated bodies so that insulation failure occurs. Accordingly, to obtain the above described mother laminated body, a plurality of ceramic green sheets have conventionally been laminated on the basis of the end surfaces of the laminated body, that is the, edges of the respective ceramic green sheets.
In the conventional fabricating method, however, a laminated body in which electrode pastes are accurately overlapped with each other in the direction of thickness cannot be obtained for the following reasons:
(a) First, the ceramic green sheets may be wrinkled, or a printing pattern of the electrode pastes may be changed due to a variation in the printing process of the electrode pastes and the elapse of time, so that electrode pastes 3a to 3c (in FIG. 2) and electrode pastes 4a to 4c, respectively printed on the upper surfaces of the mother ceramic green sheets 1 and 2, may, in some cases, be shifted, as shown in the schematic cross sectional view of FIG. 2. That is, even if the mother ceramic green sheets 1 and 2 (shown in FIG. 2) are laminated after being lined up with high precision, the electrode pastes 3a to 3c and the electrode pastes 4a to 4c cannot be accurately overlapped with each other because they are not positioned with precision; as shown in FIG. 2.
(b) Furthermore, when electrode pastes 6a to 6c (in FIG. 3) are printed and dried in a plurality of regions on a mother ceramic green sheet 5, the mother ceramic green sheet 5 is liable to warp in the vicinity of edges 5a and 5b after drying, as shown in the cross sectional view of FIG. 3. As a result, even if a plurality of ceramic green sheets are lined up on the basis of the edges of the mother ceramic green sheet 5, that is, the end surfaces of the laminated body, the electrode pastes formed on the respective ceramic green sheets cannot be accurately overlapped with each other in the direction of the thickness due to the variation in the degree to which the respective ceramic green sheet warp, as described above.
(c) In laminating a plurality of ceramic green sheets on the basis of their edges, that is, the end surfaces of the laminated body, a metallic mold 7, as shown in cross sectional view of FIG. 4, is used. More specifically, a plurality of ceramic green sheets 8a to 8f are put into a recess portion 7a of the metallic mold 7 and are abutted on an inner wall 7b or 7c with the metallic mold 7 being vibrated, to line up the edges of the ceramic green sheets.
However, the thickness of the respective ceramic green sheets 8a to 8f is approximately 10 to 30 .mu.m, and tends to be made smaller with larger capacity. Consequently, the ceramic green sheets are very thin and have no flexibility. Accordingly, in lining up the ceramic green sheets 8a to 8f by vibrating the metallic mold 7, the ceramic green sheets 8a to 8f may be broken, so that a desired laminated body cannot, in some cases, be obtained.
(d) Moreover, in order to make it easy to put the ceramic green sheets 8a to 8f into the recess portion 7a of the metallic mold 7, the width of the recess portion 7a is generally made slightly larger than the width of the ceramic green sheets 8a to 8f. Consequently, in the step previous to the step of lining up the ceramic green sheets on the basis of the edges, the ceramic green sheets 8a to 8f are liable to be laminated in a shifted state, as shown in FIG. 4.
For the foregoing reasons, in the conventional method the ceramic green sheets are not accurately laminated in the mother laminated body. As a result, in a multilayer capacitor 9 (in FIG. 5) finally obtained, an upper inner electrode 10a and a lower inner electrode 10b may not, in some cases, be accurately overlapped with each other, as shown in the cross sectional plan view of FIG. 5. Consequently, it is difficult to obtain desired capacitance. In addition, the width x of a side margin region must be made larger than necessary so as to prevent insulation failure, which prevents obtaining a smaller size capacitor and larger capacitance. In FIG. 5, reference numeral 11 denotes a sintered body, and reference numerals 12a and 12b denote outer electrodes.
Although the above description was made of a multilayer capacitor by way of example, the same problems occur in various other ceramic laminated electronic components in which inner electrodes are laminated while being separated by ceramic layers, for example, a laminated LC composite component.